this is the bead of my favourite bookmark. it is a symbol the chinese call "yin-yang" literally meaning shadow and light. it is used to describe how polar opposites or seemingly contrary forces are interconnected and interdependent in the natural world, and how they give rise to each other in turn in relation to each other.
"Yin and yang are not opposing forces (dualities), but complementary forces, unseen (hidden, feminine) and seen (manifest, masculine), that interact to form a greater whole, as part of a dynamic system. Everything has both yin and yang aspects as light could not be understood if darkness didn't exist, and shadow cannot exist without light." - wikipedia
thank you for your visits and comments; know that they are greatly appreciated.
@salza - thank you, sally.